Style and Workflow — GNUnet documentation

# Style and Workflow

This document contains normative rules for writing GNUnet code and naming conventions used throughout the project.

## Naming conventions

### Header files

For header files, the following suffixes should be used:

Suffix | Usage
--- | ---
`_lib` | Libraries without associated processes
`_service` | Libraries using service processes
`_plugin` | Plugin definition
`_protocol` | structs used in network protocol

There exist a few exceptions to these rules within the codebase:

- `gnunet_config.h` is automatically generated.

- `gnunet_common.h`, which defines fundamental routines.

- `platform.h`, a collection of portability functions and macros.

- `gettext.h`, the internationalization configuration for gettext in GNUnet.

### Binaries

For binary files, the following convention should be used:

Name format | Usage
--- | ---
`gnunet-service-xxx` | Service processes (with listen sockets)
`gnunet-daemon-xxx` | Daemon processes (without listen sockets)
`gnunet-helper-xxx[-yyy]` | SUID helper for module xxx
`gnunet-yyy` | End-user command line tools
`libgnunet_plugin_xxx_yyy.so` | Plugin for API xxx
`libgnunetxxx.so` | Library for API xxx

### Logging

The convention is to define a macro on a per-file basis to manage logging:

    #define LOG(kind,...)
    [logging_macro] (kind, "[component_name]", __VA_ARGS__)

The table below indicates the substitutions which should be made for `[component_name]` and `[logging_macro]`.

Software category | `[component_name]` | `[logging_macro]`
--- | --- | ---
Services and daemons | Directory name in `GNUNET_log_setup` | `GNUNET_log`
Command line tools | Full name in `GNUNET_log_setup` | `GNUNET_log`
Service access libraries | `[directory_name]` | `GNUNET_log_from`
Pure libraries | Library name (without `lib` or `.so`) | `GNUNET_log_from`
Plugins | `[directory_name]-[plugin_name]` | `GNUNET_log_from`

Todo

Clear up terminology within the style guide (_lib, _service mapped to appropriate software categories)

Todo

Interpret and write configuration style

### Symbols

Exported symbols must be prefixed with `GNUNET_[module_name]_` and be defined in `[module_name].c`. There are exceptions to this rule such as symbols defined in `gnunet_common.h`.

Private symbols, including `struct`s and macros, must not be prefixed. In addition, they must not be exported in a way that linkers could use them or other libraries might see them via headers. This means that they must never be declared in `src/include`, and only declared or defined in C source files or headers under `src/[module_name]`.

### Tests

Test cases and performance tests should follow the naming conventions `test_[module-under-test]_[test_description].c` and `perf_[module-under-test]_[test_description].c`, respectively.

In either case, if there is only a single test, `[test_description]` may be omitted.

## Coding style

This project follows the GNU Coding Standards.

Indentation is done with two spaces per level, never with tabs. Specific (though incomplete) indentation rules are defined in an `uncrustify` configuration file (in `contrib/uncrustify.cfg`) and are enforced by Git hooks.

C99-style struct initialisation is acceptable and generally encouraged.

As in all good C code, we care about symbol space pollution and thus use `static` to limit the scope where possible, even in the compilation unit that contains `main`.

Only one variable should be declared per line:

    // bad
    int i,j;

    // good
    int i;
    int j;

This helps keep diffs small and forces developers to think precisely about the type of every variable.

Note that :c:`char *` is different from :c:`const char*` and :c:`int` is different from :c:`unsigned int` or :c:`uint32_t`. Each variable type should be chosen with care.

While `goto` should generally be avoided, having a `goto` to the end of a function to a block of clean up statements (free, close, etc.) can be acceptable.

Conditions should be written with constants on the left (to avoid accidental assignment) and with the `true` target being either the `error` case or the significantly simpler continuation. For example:

    if (0 != stat ("filename,"
                   &sbuf))
    {
      error();
    }
    else
    {
      /* handle normal case here */
    }

instead of

    if (stat ("filename," &sbuf) == 0) {
      /* handle normal case here */
     } else {
      error();
     }

If possible, the error clause should be terminated with a `return` (or `goto` to some cleanup routine) and in this case, the `else` clause should be omitted:

    if (0 != stat ("filename",
                   &sbuf))
    {
      error();
      return;
    }
    /* handle normal case here */

This serves to avoid deep nesting. The ‘constants on the left’ rule applies to all constants (including. `GNUNET_SCHEDULER_NO_TASK`), NULL, and enums). With the two above rules (constants on left, errors in ‘true’ branch), there is only one way to write most branches correctly.

Combined assignments and tests are allowed if they do not hinder code clarity. For example, one can write:

    if (NULL == (value = lookup_function()))
    {
      error();
      return;
    }

Use `break` and `continue` wherever possible to avoid deep(er) nesting. Thus, we would write:

    next = head;
    while (NULL != (pos = next))
    {
      next = pos->next;
      if (! should_free (pos))
        continue;
      GNUNET_CONTAINER_DLL_remove (head,
                                   tail,
                                   pos);
      GNUNET_free (pos);
    }

instead of

    next = head; while (NULL != (pos = next)) {
      next = pos->next;
      if (should_free (pos)) {
        /* unnecessary nesting! */
        GNUNET_CONTAINER_DLL_remove (head, tail, pos);
        GNUNET_free (pos);
       }
      }

We primarily use `for` and `while` loops. A `while` loop is used if the method for advancing in the loop is not a straightforward increment operation. In particular, we use:

    next = head;
    while (NULL != (pos = next))
    {
      next = pos->next;
      if (! should_free (pos))
        continue;
      GNUNET_CONTAINER_DLL_remove (head,
                                   tail,
                                   pos);
      GNUNET_free (pos);
    }

to free entries in a list (as the iteration changes the structure of the list due to the free; the equivalent `for` loop does no longer follow the simple `for` paradigm of `for(INIT;TEST;INC)`). However, for loops that do follow the simple `for` paradigm we do use `for`, even if it involves linked lists:

    /* simple iteration over a linked list */
    for (pos = head;
         NULL != pos;
         pos = pos->next)
    {
       use (pos);
    }

The first argument to all higher-order functions in GNUnet must be declared to be of type `void *` and is reserved for a closure. We do not use inner functions, as trampolines would conflict with setups that use non-executable stacks. The first statement in a higher-order function, which unusually should be part of the variable declarations, should assign the `cls` argument to the precise expected type. For example:

    int
    callback (void *cls,
              char *args)
    {
      struct Foo *foo = cls;
      int other_variables;

       /* rest of function */
    }

As shown in the example above, after the return type of a function there should be a break. Each parameter should be on a new line.

It is good practice to write complex `if` expressions instead of using deeply nested `if` statements. However, except for addition and multiplication, all operators should use parens. This is fine:

    if ( (1 == foo) ||
         ( (0 == bar) &&
           (x != y) ) )
      return x;

However, this is not:

    if (1 == foo)
      return x;
    if (0 == bar && x != y)
      return x;

Note that splitting the `if` statement above is debatable as the `return x` is a very trivial statement. However, once the logic after the branch becomes more complicated (and is still identical), the "or" formulation should be used for sure.

There should be two empty lines between the end of the function and the comments describing the following function. There should be a single empty line after the initial variable declarations of a function. If a function has no local variables, there should be no initial empty line. If a long function consists of several complex steps, those steps might be separated by an empty line (possibly followed by a comment describing the following step). The code should not contain empty lines in arbitrary places; if in doubt, it is likely better to NOT have an empty line (this way, more code will fit on the screen).

When command-line arguments become too long (and would result in some particularly ugly `uncrustify` wrapping), we start all arguments on a new line. As a result, there must never be a new line within an argument declaration (i.e. between `struct` and the struct’s name) or between the type and the variable). Example:

    struct GNUNET_TRANSPORT_CommunicatorHandle *
    GNUNET_TRANSPORT_communicator_connect (
      const struct GNUNET_CONFIGURATION_Handle *cfg,
      const char *config_section_name,
      const char *addr_prefix,
      ...);

Note that for short function names and arguments, the first argument does remain on the same line. Example:

    void
    fun (short i,
         short j);

## Continuous integration

The continuous integration buildbot can be found at https://buildbot.gnunet.org. Repositories need to be enabled by a buildbot admin in order to participate in the builds.

The buildbot can be configured to process scripts in your repository root under `.buildbot/`:

The files `build.sh`, `install.sh` and `test.sh` are executed in order if present. If you want a specific worker to behave differently, you can provide a worker specific script, e.g. `myworker_build.sh`. In this case, the generic step will not be executed.

For the `gnunet.git` repository, you may use "!tarball" or "!coverity" in your commit messages. "!tarball" will trigger a `make dist` of the gnunet source and verify that it can be compiled. The artifact will then be published to https://buildbot.gnunet.org/artifacts. This is a good way to create a tarball for a release as it verifies the build on another machine.

The "!coverity" trigger will trigger a coverity build and submit the results for analysis to coverity: https://scan.coverity.com/. Only developers with accounts for the GNUnet project on coverity.com are able to see the analysis results.

## Commit messages and developer branches

You can find the GNUnet project repositories at https://git.gnunet.org. We do not maintain a separate ChangeLog file anymore as the changes are documented in the git repositories. Commit messages are required to convey what changes were made in a self-contained fashion. Commit messages such as "fix" or "cleanup" are not acceptable. You commit message should ideally start with the subsystem name and be followed by a succinct description of the change. Where applicable a reference to a bug number in the bugtracker may also be included. Example:

    # <subsystem>: <description>. (#XXXX)
    IDENTITY: Fix wrong key construction for anonymous ECDSA identity. (Fixes #12344)

If you edit files that change user-facing behaviour (e.g. header files in src/include) you will have to add at least one line in the commit message starting with "NEWS:". If there is a special reason why you deem this unnecessary, you can add the line "NEWS: -". Any "NEWS" lines from commit messages will on release be put into the “NEWS” file in the tarball to inform users and packages of noteworthy changes.

    # NEWS
    NEWS: The API for foo has changed: lorem ipsum.

Note that if you run "./bootstrap" hooks will be installed that add message hints to your commit message template when you run "git commit".

If you need to modify a commit you can do so using:

    $ git commit --amend

If you need to modify a number of successive commits you will have to rebase and squash. Note that most branches are protected. This means that you can only fix commits as long as they are not pushed. You can only modify pushed commits in your own developer branches.

A developer branch is a branch which matches a developer-specific prefix. As a developer with git access, you should have a git username. If you do not know it, please ask an admin. A developer branch has the format:

    dev/<username>/<branchname>

Assuming the developer with username "jdoe" wants to create a new branch for an i18n fix, the branch name could be:

    dev/jdoe/i18n_fx

The developer will be able to force push to and delete branches under his prefix. It is highly recommended to work in your own developer branches. Code which conforms to the commit message guidelines and coding style, is tested and builds may be merged to the master branch. Preferably, you would then...

- ...squash your commits,

- rebase to master and then

- merge your branch.

- (optional) Delete the branch.

In general, you may want to follow the rule "commit often, push tidy": You can create smaller, succinct commits with limited meaning on the commit messages. In the end and before you push or merge your branch, you can then squash the commits or rename them.